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April 24, 1928.

J. E. CALVERLEY ET AL BLECTRI C CONVERTI NG APPARATUS ?25 S Sheets-Sheet I Filed Nov. 12,

Armcwb April 24, 1928.

J. E. CALVERLEY ET AL ELECTRIC CONVERTI NG APPARATUS Fil Nov 1 1925 3 Sheets-Sheet 2 April 24, 1928.

J. E. CALVERLEY ET AL ELECTRIC CONVERTING APPARATUS Filed 1925 3 Sheets-Sheet 3 Y to. a direct current system. For convenience .:of. discussion .the alternating current system .first'imentionedabove will be spoken of as Patented Apr. 24, 1928.

NITED STATES PATENT FFICE.

I J 'OHN EARNSHAW CALVERLEY, OF PRESTON, AND WILLIAM EDEN HIGHFIELD, OF

LONDON, ENGLAND, ASSIGNORS TO THE ENGLISH ELECTRIC COMPANY LIMITED,

OF LONDON, ENGLAND.

ELECTRIC CONVERTING APPARATUS.

- This invention relates-to apparatus used for conversion. from alternating current to drrectcurrent or' vice=,\-'er-sa of the kind in which ,a. normal polyphase system 4 generally .ofia.-'1elativel y-small numberof phases, for jinstance three, is associated through the me- ;dium of a number of transformer cores with .ario'ther.polyphasesystem 1Whicli -n'iay be of a materially higher number of phases-and is connected to commutatmg gear and thereby the prin'iaryIsystemand the other system will be spoken of as the secondary system. these termslbeing-used for the purpose of distinsguishi-ng the-systemratherthan for the puraposezof indicating thein functions. xForothis .apurpose offiassociation with the commutatinggear the windings. forming the secondary. system.-are arrangedvto form a symmetrical'rclosed ring Winding from which are taken at. 5? approximately equi-distant .points aset;of. tappingsleading-to com- -1nutator"seg1nents.- Iii-general these seg- 'ments are stationary andcommutation is effected by therotation of brushes, the movement ofwhich has tobe-synchronized with the a lternat-ion of "current in :the' secondary system. I 1 .I

- Apparatus of-the kind above referred to is (1830 lined in :the following specifications British Patent No. 140.853. United States Patents Nos. 113250.554- and 156L032. and British Patent No. 184,259. It has also been described .in technical journals under the name :of 'lransverter" see for instance Engineering .published in London May 2nd 1924.

- The object of the presentinvcntion is to attain and maintain stable working of such apparatus. by providing-at all times a balanceofampere turns acting on each trans former-score. without distortion or disturb anceof t he flow of current either in the alternating or direct current circuits of the RPPRIZItUS'" i 1 The invention will be further described by all refer to an' example ofthe apparatus 'which is described in the more recent of thc 68,588, and in Great Britain December 10, 1924.

publications mentioned above in which the .alternating or primary system consists of .three phases and the secondary system condsi sts of thirty-sixphases, the trans lormathm being effected by means of 'eightcmi cores. These.eighteencores (not shown in the accompanyingdrawing-s) are assumed to be 'numbe'red L-IES and these numbers enclosed incircles and the same numbers with the lindex letter A are used to indicate winding ,sections each of which is either located on the core the number of which it bears or is directly related to a winding mounted there on as will be explained hereinafter. I The three figures of the drawings have similar. diagrammatic characteristics which may be most readily introduced by reference to Figure In this the secondary winding ,is indicated vectorially by a thirty-six sided .polygon S forming' the outer part of the .diagram, the 'positions of the positive and .negative :brushes for .the direct current in relation. to this winding are shown,- the. .brushes being located atthe top and bottom ,offgthe diagramrespectively. Each of the thirty-six sections of this winding comprises thesame number of turnsand twov sections are located .on each of the cores as is indicated by the occurrence in the thirty-six .sided polygon of eighteen pairs ofsides, themembers of each pair being located dian' etrically opposite. to each other and one haringa reference numeraL for instance, 1. and the other the same numeral with the index letter .A., The phase relations-Input 'the sections of the secoudar winding is shown by theangular relationships oi. the ,sides of thepolygon and by the arrow heads Cir as a thirty-six sided equi-latcral polygon in- ;dicate-s. that'the secondary windings are connected endto end to form a closed ring windingiu each section of which is an alternating electro-motive force equal in magnitude with thatin each of the other seetionsthe phase difference between adjacent sections being constant throughout the ring which,is therefore electrically symmetrical. In; this connection it. is pointed out that while the arrow heads on corresponding .w in d ings--on the two sides of the diagram, for instance, 1 and 1 1"- point in parallel directi.ons, that is,'-\ erticz illy upward in the case mentioned, these two sections are actually in oppositioirof "phase as shown bythe fact that they oppose e'ach "other'hr'ound the closed circuit formed by the secondary winding. In each halfpi this winding (considering it to he'divided by't-he brushes-into two halves) there is found a section having an electric-motive force equal in magnitude and opposite in phase to e'a'clVofthe sections in theother half. This of course is anesin effect this seeondary wint ling is I I Y l are ol unequal length.

make clear hythis-tigure; further (lillerence' that -the 'eonditionwassinned in Figure l a'rel'those which existwat-a "sli htly 'ear-lier jihn'se posit-ient han"that 0f minimis ng YB am e. The

' Figure l'nlzd' 'a'hase 16bei'ngin that' position deem-my "s'h'ow'" thaseq'aeme "in iwliich I etions re-'eenneeted. -T;hat

"passage" of the-sine Wave of= the-frmelamen l tal frequency. By this -meansu balance-of synuuetrieal alul to be parallel with the corre spomline sections of the secomlary winding of the hem-(rs. lt will he noted that the rectors forming the outer part of the figure I v This is of course due to the fact that the-nun'l berof turns er each section of the rimaly winding varies from core to core.

In Figure 1 11 similar showing of the secolulaiy asul prin'iary windings 0f the main t'iansforrners hasbeen"adopted-butpart has been lH'OliOll away for convenience in setting out the oth'enfeatures'which it-is 'rlesiretl to There 1S1 also the Fr ire 3,'phase 13 ofthe se'contlaryiw intl mg being "in the *posltron for commutation an Efrain S andportions 0f theformefhave been broken away t )a'eco11'11'noclate thela'tter.

' The brushes-also'have been omitted.

\Vhen conversiowappaaatus "of thistype-is working, tlie 'pri'1nary" \v'inding' or tinelings l on each transfori'ner-corewill un olerftho lliOfit satisfactory conditions "of "operation carry a eurrent whiclr has a wa-veiformaapproximately sinusoidal. Ass\.1ming'ithat-.the

load -ou'the clireet'ciurentrside-of the(apparatus is steatlygthere' will flow throughithe brushes aeurrent of con'stant' value aznd :this

form of the eurr'euti in the connections-flie tween those sections of the seeoiula ry' winding; and theeo'muiutatorsegments,"there will not oceur at each instant a balanee of -am perrturns on the core due to tlle dCtlOH'Of these two windings. -'B \f" 1.he preeentinventron the difficulty is (lealt-with hy providrng a. h yeqwnss circuit for eaehsection of'the seeoiulary \vmchng'ftluserr'cuit having-such 'el'iaraeterisites that. it permits the=passage of a current*haviuQ a'wvave t'orn'i suhstantially equal to the diflereuce between the-sinusoidal ware and the rectangular wave previously mentmned.- "Af-the siatne tamevthe;1bye"- j ass circuit-opposes considerablen'npedance to the.

ampere turns at allpoints in'theicyele ex-i'sts at each transformer 'eore and-thereby distorlht) tion of the wave forms of bothcurrents and increases.

E. M. F. in the secondary circuit which would otherwise occur isavoided.

The bye-pass circuits may be coupled with the secondary winding either directly, that is, by conductive means, or inductively. Figure 2 shows an example where conductive coupling is employed. If we consider in connection with this figure core No. 1 of the transformer arrangement, we see. that in accordance with the; preceding description it has on ita primary coil, P indicated .by 1 and two secondary coils .3. indicated by 1 andli-JVith each ofithe-latteris connected by means :of tappings-T (taken oft atthe j unctions.between=;the coils 1. and 1?..and 5 the adjacent sections lot. the secondary winding) a section U-ofthe bye-pass ivindingi, Every other section of'the secondary.;.winding .S also 11218: a. .bye-p ass, winding similarly associated .with ,it by means-of: the;ta'ppings- T. There iarezaccordingly thirtyrsixiigroups of coils in the bye-passzwindingicorresponding to the thirty six sections.;of,the secondary .winding. Of these -ithirtyrsix. groups.- six indicated by U consist of-a single'coil. Each offlthe other thirty groups consists of two parts. These twolparts are indicated by the two :lines-V-between :adjacent tappings T, their resultant being-shown by a broken .line.

.It. ;will.be seen that we have provided-in conductive connection with: eachqsection of the secondary winding a b'yevpass winding'U or group of windings V sothat current can flowthrough the-bye-pass circuit to .the commutator without passing through. the secondarv. winding. It-will therefore. be seen that we haveiprovided circuits: which permit of a current of .sine wave -for1n.in the :primary.winding or windings of a core-to'be balanced at each instant, as regards the arm Dere turns produced, by theucurrentflowing in thesections. of the secondary .winding on that-corewhole current of rectangular wave form is being taken throughthe-commutator connectors to the direct current terini-' nals of the apparal us. The secondary windin; sections then. must carry current of sine wave form and the bye-pass circuit must carry a. current having a wave form substantially equal to the [difference between the sinusoidal 1 wave and the rectangular wave. It remains to be shown how the secondarv winding sections and the bye-pass winding sections respectively are made selective as regards the current wave; forms so as to obtain an appropriate division of the commutated direct current between thenr. To recognize what this implies it must be remembered that the rectangular waveofcurrent iftormed .ot a fundamental'sine wave .of v the same frequencyas-the Iprimary current and an infinite series of harmonics the amplitudes of which decrease rapidly as. their frequency The result to be attained therefore is the division of the commutatcd direct current in such a way that the fundamental sine wave passes through the secondary Winding S while the harmonics are byepassed through the winding sections U and V. The passage of the bye-pass current represents a certain amount of electrical power and it is necessary therefore to provide meansior giving to and taking from the secondary circuit by way of the bye-pass circuits the amount of energy represented at each instantby the harmonic current which it is desired to bye-pass. Since, however, the

total powenrepresented by the currents in all the .bye pass circuits of the apparatus at any instant iszero, this requirement may be met. byarranging means for transferring energy between the several winding sections U and'V of the bye-pass circuits.

:This is ca rried outaccording to the present invention by forming the bye-pass circuits of-windings arranged in an appropriate manner. on the cores of a transformer or a group of transformers. The arrangement of-this part of the apparatus which is shownsin Figure 2 of the accompanying drawings is one in which a three-phase transformeris used having .on each of its cores bye-passcircuitsso formed as regards their respectivenumber otturns and so gl'OllPNl as; regards theirrespective phases in the secondary system that the total number of ampere turns on -any one core at any instant is approx imately z erof- The three-phase arrangement ptthe cores (although these are not -shown) .will .be recognized from a consideration of that part of the diagram which shows the bye-pass windings U, V. It will be seen that all the lines indicating these windings are drawn parallel to three directions, namely, the horizontal direction and two directions at 120 thereto. It is to be understood that the direction of these lines shows which of the three cores the winding sections are mounted on and the lengthsof the lines indicate the proportiouate number of turns in the section. The grouping and. dimensioning (as regards number of turns) of the individual sections of this winding of the auxiliary transformer will be seen to be similar to those employed for the primary windings oi the main transformers except that cach section is duplicated in the case of the bye-pass winding so as to provide a thirty-six phase arrangen'ient corresponding to the thirty-six phases of the secondary winding S. In the case of the primary.windiugs ot' the main transformers a three-phase supply is dis tributed over eighteen cores, being for that purpose changed. to. an eighteen phase system, three phases of which correspond with the phases of the external primary system and each are formed by a single coil, while over lihc vhusc. -2mgles botwlien t'hsc lllTlO phases and are each formed by two 'c'oilx. This distribution of the. primary windings is .clciu'ly set out in the prior puhl -icati'ohS i hariisevfim passciicuitsjmay also huconsidered as the gelncxit will' iilsdli ave" the aklvan-j of symmetry in the potential relation of the tapping points. irregularities of the kind indicated may occur due to the difliculty of splitting up the primary system into sections each comprising an appropriate number of turns owing to the fact'that'fract'ions of turns-cannot of course be employed. An additional three-phase winding \V forming a delta which is connected to the three-phase supply by the leads X is arranged on the auxiliary transformer. This serves to 'sup-' ply energy to the synchronous motor during starting. During running the energy for the motor may be supplied from the main transtorn'iers through the secondary winding and the connections between this winding, the bye-pass windings and the'armature winding M. If, however, the winding Vis left in circuit with themains during the running of the apparatus, it provides an ternative path for feeding the motor.

In manylcases,'ins' tead of'the direct coupling o'f the bye-pass'windings with the seeondary 'windings, it will be preferable'to use an inductive connection. Examples of this are shown in Figures 1 and 3;. Referring particularly to Figure 1 it will be seen that thereare provided additional windings D which are' spoken of as compensating coils. "Each one of these-coils is mounted on one of the main'cores, (the 'eoil indicated by '1 being on the'transformer core 1') which, as"p'rev iou'sly' indicated,-'carries ons or two primary windings as the easemay be and two secondary windings (corresponding for instance tothe vectors 1 and 1 As shown in Figurel the-compensating; coils D a're grouped to form six deltas so that these windings are capable ofactmg as a low 1mpedanee path for harmonics-of three time s and multiples of three times the fundamental frequency so that these compensating coils take the place of the additional windings previously referred to in connection with our Patent No. 1,567,032. coils are connected through the wires L with windings mounted on the auxiliary trans-- These windlngs form a SGIIQSOT- former. deltas indicated ve'cto-rially'v by E which correspond withthe six deltas formed by the compensating coils. It is tobe noted, however,'that the actual arrangements of the coils forming these two sets of deltas is not the same. In the case of the compensating coils we have eighteen similar coils each arranged ona' separate :core. :In the auxiliary transformerit-here areonlyiithree cores and accordingly. thedeltas have-to be .built up from thirty-three coils which arearrangedv to form eighteen groups eachcorresponding to one of the c'ores of the main transformersystenn Three of these groups are formed each of-a single coil and'the other fifteen are each formed of-two coils taken from different The compensating positions of some of these groups'are indicated by the broken line F. The grouping and dimensioning (as'regards number of turns) of the individual coils of this winding of the auxiliary transformer will be seen to be similar to those employed for the primary windingsof the main transformers as modified to deal with the different conditions of the bye-pass windings E which have been discussed-in connection with the wind ings U, V of Figure '2. There is, however, this difference between the case of Figure l and Figure 2 that in the former we have only eighteen phases as against thirty-six in the latter. This avoids the duplicationof coils. The synchronous motor M is :in this case as in the case of Figure 2 connected to the wind ings on the auxiliaryrtransformer'. In the present case the conneetion is made to oneof the deltas,-:namely ,-l, 7, 13,'each side of which represents a single 'winding.- During the starting. up =ofnthe'1apparatus this delta can serve as -'.tl1e :secondary'/ winding of a transformer having. ith primary: winding N which is connected torth'emains'. :The .func-' tion of this winding EN is. similars to that-of thewinding-.WofFiguTe 2, that; is to say, it is principally, arequired kfOl' starting and Imay be put out ofcircuit afternth'e apparatus-has reached normalworkin'g conditions when the energy for driving ,tl1eimotor-.M,may reach it by, -.=way.-of. the windings Dion-the main transformers andthe connecting wir'es L. It will be noted thlhin the figure breaksihave been5shownfin'these;wires; ,This is to .'be taken as.-indicatingi fthat the io'i'rcuits 'may .be broken atthese. points byl -means'ozf switches B .so that the motor may .be isolated from the main ;trans forlii ers during starting if. rcq e 1 "uld'z -j :Hzili .ti. -:l :E-

I'm-.will be recognized that the-inductive couplingbetween the bye-pass windingE and the secondary winding S byway of; thecompensating coils ,D is closely: equivalentito the conductive; connectionas illustrated in the example shown in Figure 2. -At the same Y time, it has certain. practical advantages, for instance, 'that the voltage of the windings on the auxiliary transformer 'isindependent of the voltage of the secondary system andthe number of bye-pass windingsections need only-,be made equal to the number of cores in the main transformer system-and not to the number, of sections inthe secondary winding. Y

The bye-pass. e-tfect'isbrought ;about 1 in a somewhat different way in the case ot-Fig ure- 1 than that-described in connection with Figure *2. As there is noconductive conneetionEbetwee'n the secondary winding and 1 any other :winding, -it-- is'iobviousthat the currentin the secondary windingS of F igure 1 must have the Same wave form as the current w'hich passes through the commuter tor connectora-that isto say, a rectangular viding a separate winding on the auxiliary transformer.

What we claim as our invention and desire to secure by Letters Patent is l. A polyphase transforming arrangement comprising a set of windings forming an electrically symmetrical closed ring and connected to commutating gear, by-pass circuits arranged in connection with the said set of windings and including coils grouped together on transformer cores to form an auxiliary transforming arrangement, the grouping being such that the by-pass circuits offer a relatively low impedance to harmonic currents and a relatively high impedance to currents of fundamental frequency, substantially as and for the purpose set forth.

2. A polyphase transforming arrangement comprising a set of windings forming an electrically symmetrical closed ring and connected to con mutating gear, an auxiliary transforming arrangement consisting of a polyphase transformer core structure and coils thereon, by-pass circuits arranged in connection with the sections of the said closed ring, winding, the said by-pass circuits including coils on the auxiliary transformer the said coils being so formed as regards their respective number of turns and so grouped as regards their respectixe phases that the total number of ampere turns acting on any one core of the auxiliary transformer due to the by-pass current at any instant is approximately zero, substantially as described.

3. A polyphase transforming arrangement comprising a set of windings forming an electrically symmetrical closed ring and connected to commutating gear, by-pass circuits arranged in connection with the said set of windings and including coils grouped together on transformer cores to form an auxiliary transforming arrangement, a synchro nous motor for driving the connnutating gear and means connecting the armature winding of the synchronous motor with the by-pass coils on the auxiliary transforming arrangen'ient, substantiall as described.

4. A polyphase transforming arrangement comprising a set of windings forming an electrically symn'ietrical closed ring and connected to commutating gear. by-pass circuits arranged in connection with the said set of \\'iudings and including coils grouped together on transformer cores to form an auxiliary transforming arrangement. and conductive connections between the hy-pass coils of the auxiliary transforming arrangement whereby they are joined together to form a closed winding.

5. A polyphase transforming arrangement comprising a polyphase core structure, a set of windings one on each of the cores of said structure, said windings being grouped together conductively to form an electrically symmetrical closed ring which is connected to commutating gear, a compensating coil on each of said cores and bypass coils conductively connected with said compensating coils and grouped together to form an auxiliary transforming arrangement, and grouping being such that the bypass circuits otfer a relatively low impedance to harmonic currents and a relatively high impedance to currents of fundamental frequency, substantially as and for the purpose set forth.

6. A polyphase transforming arrangement comprising a polyphase core structure, a set of windings one on each of the cores of said structure, said windings being grouped together conductively to form an electrically synnnetrical closed ring which is connected to commutating gear, a compensating coil on each of said cores, said compensating coils being connected in delta groups, and by-pass coils conductively connected with the junctions of said compensating coils and grouped together to form an auxiliary transforming arrangement, the grouping being such that the bypass circuits offer a relatively low impedance to harmonic currents and a relatively high impedance to currents of fundamental frequency, substantially as and for the purpose set forth.

7. A polyphase transforming arrangement comprising a set of windings forming an electrically symmetrical closed ring and connected to commutating gear, a compensating coil inductively associated with each winding of said set, a by-pass winding conduc tively connected across each of said compensating coils, the said bypass windings being grouped together to form an auxiliary transforming arrangement, the grouping being such that the bypass circuits offer a relatively low impedance to harmonic currents and a relatively high impedance t0 currents of fundamental frequency, substantially as and for the purpose set forth.

8. A polyphase transforming arrangement comprising a plurality of three-phase transformer core structures, a set of windings having one section on each of the cores of said structures, the said windings being interconnected to form an electrically symmetrical closed ring which is joined to commutatiug gear, Irv-{pass circuits arranged in cmniection with said set of windings and including coilsgrouped together to form an auxiliary transforming arrangement and mounted on the cores of one of the said three-phase transformer core structures, substantially as described.

In testimony whereof we allix our signatures.

JOHN EARN SHAW CALVERLEY. \VILLIAM EDEN HIGHFIELD. 

